The present invention relates generally to the production of 3-cyanopyridine and in particular to a process which involves the direct ammoxidation of 2-methyl-1,5-pentanediamine, alone or in admixture with 3-methylpiperidine, to 3-cyanopyridine.
As further background, the manufacture of 3-cyanopyridine and other pyridine derivatives has been and continues to be of major commercial interest on a variety of fronts. For example, 3-cyanopyridine is an intermediate to a large number of agricultural and pharmaceutical products. A number of known processes for preparing 3-cyanopyridine and other pyridine derivatives involve catalytic cyclization and dehydrogenation reactions. Many such reactions are reviewed by Brody and Ruby in Volume 1 of Pyridine and Its Derivatives, E. Klingsberg, ed., and most recently by Bailey, Goe and Scriven, in Vol. 5 of the Supplement to Pyridine and Its Derivatives, G. C. Newkome, ed. These reactions have generally been carried out in the gas phase at low to moderate temperatures up to about 400.degree. C. using predominantly precious metal catalysts such as palladium and platinum.
For example, British Patent No. 755,534 issued in 1956 to ICI describes the conversion of pentanediamine (PDA) to pyridine in 55% yield using a catalyst of 5% platinum on a silica support at 400.degree. C. This patent also reports the conversion of PDA to piperidine using acidic heterogeneous catalysts such as silica, silica-alumina beads and boron phosphate, without the precious metal or any other metal component at 350.degree. C. Other examples include the following:
Netherlands patent application No. 7,005,792 (Deumens, Groen, and Lipsch, 1971 to Stamicarbon; Chem. Abstr., 76, 46099) reports converting PDA to piperidine in high yield using a catalyst of Raney-nickel supported on silica or to various mixtures of piperidine an d pyridine using a catalyst of palladium supported on alumina at 125-300.degree. C.
U.S. Pat. No. 4,086,237 issued in 1978 to Dynamit Nobel (equivalent to German Patent No. 2,519,529) reports the conversion of 2-methyl-1,5-pentanediamine alone or with 3-methylpiperidine to mostly 3-methylpyridine using palladium metal on an alumina support at 200-400.degree. C. U.S. Pat. No. 4,401,819 issued in 1983 to Rhone-Poulenc reports a similar conversion using a precious metal on a particular macroporous solid silica support at 200-500.degree. C.
British patent application No. 2,165,844 filed in 1986 by ICI reports the eventual conversion of glutaronitrile to pyridine, perhaps with the preferred isolation of 1,5-pentanediamine as an intermediate, using palladium metal on silica support at 350-400.degree. C.
Collectively, these references show that pentanediamine and its alkyl derivatives have been selectively converted in the past to their piperidine counterparts using catalyst supports alone or in combination with the Group VIII metal, or to admixtures of these piperidines and their pyridine counterparts using various Group VIII precious metals (also called noble metals) including palladium and platinum at temperatures of about 400.degree. C.
Specifically with regard to the ultimate preparation of cyanopyridines, this cyclization and dehydrogenation work has suffered since in large part it has focused upon the production of methylpyridines, which must be converted in subsequent manipulations to cyanopyridines. U.S. Pat. No. 5,028,713 does disclose the conversion of 2-methylglutaronitrile to 3-cyanopyridine. However, both the reported yields and those obtained in the applicants' comparative work set forth in the Examples below are extremely low, making this process unattractive for commercial scale production.
Thus, especially with respect to cyanopyridines, there has been a growing need and economic driving force for an improved route to cyanopyridines starting with methyl-1,5-pentanediamines. The present invention is addressed to this need.